Television system



V. K. ZWORYKIN TELEVISION SYSTEM Filled July 25, 1936 July 2, 1940.

Patented July 2, 1940 TELEVISION SYSTEM Vladimir K. zworykimrhnaaelphia, 12a-Q, assigner` to Radio Corporation of America, a corporation of Delaware i Application July 25, `1936, Serial No. 92,565;`

4 Claims.

particularly to television systems` for, two-way` transmission and reception.

An object of my invention is to provide animproved two-Way television system. which requires only a single transmission channel.

A` further object of my invention is to provideL an improved single channeltWo-way television system in which cathode ray `tubes are employed' for both transmission and receptionl A still furtherobject of my inventioniis to pro vide` an improved television system which may be employedeither for two-Way transmission of picturesoi reasonably good quality or for one-way transmission of pictures of excellent quality; l

In practicing myinvention, similar apparatus is employed at each `end of' a single communica-` tion channel. `Preferably the apparatusV atk one end of the channelis identical` with the appara-` tus at the other end of thechanneli The apparatus at each end ofthe channel includes a cathode ray transmitter tube, aicathode ray. rav ceiver tube and terminal equipment comprising-a deiiecting circuits, amplifiers', etc. Synchronize.,n

\ tion of the cathode ray deflection at eachA end of the channei is maintained by means of impulses supplied from a synchronizing generator which:

may be included inonesetroi terminalequipment Preferably, the synchronizing generator supplies horizontal synchronizing impulses and vertical synchronizing impulses having such `frequency relation to each other thatinterlaced scanning is produced as described in U. 55.* Patent No. 2,178,218, issued Oct. 2l; 1939, to Aida V. Bedford and assigned to the America.

. At` each end or terminal of the communica A i other terminal being effective to transmit and reproduce pictures While thecther transmitter tube and receiver tube are ineffective.

The invention will be betterunderstocd` by referring. to the single figure of `the-drawing wherel s single communication channel, such as a wire line, is indicated at i. Atene endof the `line the transmitter and receiver tubes are indicated at 2` and 3, respectively, the transmitter tube being,-`

provided With a suitable camera 5; 'Terminal api paratus is indicated` at` I 9.

Radio` Corporation oil My invention relates to television systems and' At the other end of the line acompleteztransv4 mitting and receiving unit*I is shown in more def-1 tail, the; terminal apparatus being shown by ai block diagram. This unit includes a cathoderayaI transmitter tube Il` and a` cathode ray receiver tube 6. `The transmitter: tube may beanyqo-ner of several Well known types, suchas the tube` described in British Patent No; 369,832, issued March 31, 1932, this being the tuoe`i11ustrated1in` the"drawing.v It includes an evacuated envelope having therein an electrongun l for producing a` cathode ray,` a light sensitive `mosaic il1 and, screen electrodes Sand II. Whenav picture is projected upon the front side` of the mosaic E: While the back side ofl themosaicisbeingscanned by the cathode ray picture; signalsfappear acrossf an outputv resistor i2. Thelreceiver tubeimay:` be of a Well known typev including an evacuated' envelope having therein an electron gun I3 and,` a fluorescent screen I4.

Each cathoderay tube isprovided with suitable means for deecting the cathode ray both hori4 zontally at a comparatively highl frequency and vertically` `at a comparatively low, frequency si.- multaneously for effecting scanning. In theI specic,` apparatus illustrated, the transmitter` tube 4 is,` provided'with vertical ldeflectingv coils l6f and horizontal deecting coils il, While the receiver-'tube Eis provided with vertical delectingA coils I8 and horizontal deflecting coils I9. The two; pairs of horizontal deiiecting coils may be supplied from-1a` single horizontal deflecting cire iti cuit ZfI: Whichmay be of; any suitable type,y suchA i as` the deflec-ting circuit described in Tolson Patent 1,999,378. Likewise, the` vertical, deflect-I ing coils-may be supplied from a singleuverticalf deiiectingcircuit 22 which` also may beI of' then typedescribed in theabove-mentioned Tolson patent. o i

` Synchronous deflectionof the4 cathode rays inthe two cathode ray tubes Il and 91 is p maintained byfmeans ofapparatus including a synchronizing generator indicated at 23.-` This synchronizing generator may be o1` the type described and. claimed in thevabove-mentioned Bedfordapplica-r tion; Inrorder to make the invention more easily understood, specific frequencies have been as,-I sumedfo-rtlie horizontal and vertical synchronizing impulses as indicated 'on` the drawing'. As previouslymentioned, it ispreferred that these synchronizing impulses` bear such a relation to eachother that interlaced scanning is produced. As, pointed out in the above-mentioned Bedford application; this'xfrequency relation preferably isA such that; theI vertical deflectingr, frequency' goes into the horizontal deiiecting frequency a whole number of times plus one-half.

The synchronizing impulses are supplied through a suitable amplier 24 to a filtering or separating circuit 26 such as described in British Patent 407,409, whereby horizontal synchronizing impulses are supplied tc the horizontal deflecting circuit 2l and vertical defiecting impulses are supplied tc the vertical deflecting circuit 22.

It will be understood that the synchronizing impulses are also transmitted over the communi-y cation channel l to maintain the cathode ray deflection in the transmitter and receiverl tubes 2 and 3 at the other end of the line in synchron nism. Thus it will be seen that the deflection in such cathode ray tube is in synchronism with the deflection in the other cathode ray tubes. Also it will be understood that the system described up to this point would produce .pictures l.

' complished by supplying the picture signal appearing across the output resistor I2 to the input circuit of a blanking out amplifier 21 which may be of the type described in U. S. Patent No. 2,092,496,issued Sept. 7, 1937, to Harry Branson and assigned to the Radio Corporation of America. The output circuit of the blanking out amplier`21 is connected to the line i whereby picture signals may be transmitted to the receiver at the other end of the line except during the periods that a blanking impulse is being im supplying picture signals from the line I to the input circuit of a blanking out amplifier 28, whichv also may be of the type described in the Branson application. The output circuit lof the amplifier 28 is coupled to the input electrodes of the cathode ray tube B. l

Suitable blanking out impulses may be produced by supplying sixty cycle vertical synchronizing impulses to a blocking oscillator 29 adjusted to produce impulses at the rate of 30 per second in synchronism with'the sixty cycle impulses. Such a blocking oscillator is described'in the above-mentioned Tolson patent. The thirty cycle impulses may be converted into a thirty cycle sine wave as indicated at 3| by passing them through a tuned amplifier 32. The sine wave may then be converted into rectangular impulses as indicated at 33 by passing it through clipping tubesy 35. "The clipping tubes may consist of two tubes connected in cascade, each tube being biased beyond cut-olf. Or, if preferred, the rectangular impulses may be produced by impressing upon amplifier tubes sine waves of such amplitude that the tubes are driven to plate current saturation.

It will be apparent that with respect to the alternating current axis of the rectangular impulses 33 there is a positive rectangular impulse lasting for one-sixtieth of a second and a negative rectangular impulse lasting for the same period. The period of one-sixtieth of a second is, of course, the period of one picture frame.

Therefore, these rectangular impulses may be employed for making the blanking out amplifiers 21 and 28 ineffective for transferring signals for the duration of one picture frame. These impulses may be applied through a switch 34 and a conductor 36 to the blanking out amplier 21 in the transmitter output circuit. Each negative impulse applies such negative polarity to the amplifier 21 as to block it and prevent the transmission of picture signals.

The blanking signals indicated at 33 are passed through a polarity reversing amplifier .31 and supplied to the blanking `out amplifier 28 in the receiver channel whereby those impulses which are Apositive at the transmitter amplifier 21 are negative at the receiver amplier 28 and of vsufiicient 'amplitude to block it and thereby prevent the transmission of picture signals. It will be evident that this causes the blanking out amplifiers 21 and 28 to be rendered ineffective alternately, whereby the receiver tube 6 may receive picture signals from the transmitter at the other end of the line without simultaneously receiving picture signals from the transmitter tube at its own end of the line.

From the foregoing description it will be understood that two persons at opposite ends of the line may see each other simultaneously, each person seeing a picture made up of thirty picture frames per second.

It will be understood, of course, that when two views are being seen simultaneously, the View is not an interlaced picture and will, therefore, be of poorer quality than the system is capable of providing.

However, it is a simple matter to so adjust my system that an interlaced picture may be transmitted in one direction when a high quality picture is desired. This may lbe accomplished by rendering the vblanking impulses ineffective at each end of the line as by openinga switch, such as the switch 34, in the line supplying the blanking out amplifiers with blanking signals. If it is desired to transmit a picture from the terminal apparatus 3 to the receiver tube 6, the output circuit of the transmitter tube 4 is opened as by opening a switch 38. In this position, a person at the receiver tube 6 will see the person -at the transmitter tube 2 and the person at that ode ray is cut-off and the tubes are ineffective for transmission or reception.

It will be apparent that various other modifications may be made in my invention without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and are set forth in the appended claims..

I claim as my invention:

l. In a television system, a single communication channel, a cathode ray transmitting tube land a cathode ray receiving tube at one end of said channel, a second cathode ray transmitting tube and a second cathode ray receiving tube at the other end of said channel, means including a generator of synchronizing impulses for so deflecting the cathode rays in said tubes that the lines scanned during one picture frame fall between the lines scanned during the preceding picture frame to producev interlaced scanning, blanking means for rendering said iirst transmitting tube and said secondreceiving tube ineffective for transmitting and receiving pictures and effective for transmitting and receiving pictures alternately at a rate at least equal to that of persistence of vision and for simultaneously rendering the other of said tubes alternately effective and ineiective for transmitting and receiving pictures, said iirst transmitting tube and said second receiving tube being ineffective when said other tubes are effective, means for making said blanking means ineffective and for making one of said transmitting tubes ineffective for transmission for the duration of a one-Way transmission Whereby an interlaced picture is transmitted and received.

2. In a television system for picture transmission, a single communication channel, terminal apparatus for one end of said channel, said apparatus comprising a cathode ray transmitting tube and a cathode ray receiving tube, two blanking out amplifiers, said transmitting tube being connected to said channel through one of said ampliiiers, said receiving tube being connected to said channel through the other of said ampliers, means for deiiecting the cathode rays in said tubes horizontally `at a comparatively high frequency and verticallyat a comparatively 10W frequency to eiiect scanning, means for producing rectangular electricalimpulses occurring in iiXed time relation to said vertical deflection, and means for so impressing said rectangular impulses upon said blanking amplifiers that they are rendered ineffective alternately to transmit picture signals.

3. In a television system for picture transmission, a single communication channel, a terminal unit at each end of said channel, each unit comprising a cathode ray transmitting tube and a cathode ray receiving tube, a plurality of coupling circuits, said tubes being connected through said coupling circuits to said channel for the transmission and reception of picture signals thereover, means for so deecting the cathode rays CII in said tubes that the lines scanned during one l circuits that said tubes are rendered ineffective alternately to transmit and receive picture signals. n

4. The invention according to claim 3 characterized in that additional means is provided to make said rectangular impulses `ineffective and for making said transmitting tube ineffective for transmission for the duration of a one-way transmission whereby an interlaced picture is transmitted and received.

VLADIMIR K. ZWORYKIN. 

